Lightning is one of the top three storm-related killers in the United States, according to the National Weather Service, but it is also one of the least understood weather phenomena.

Each event, however, certainly starts with a growing thunderstorm cloud, a negative charge building in the bottom of the cloud and a positive charge in the ground below. When the difference between charges grows too great, the insulating capacity of the air breaks down and electricity is discharged.

Bolts of electricity — each can carry up to 200 million volts — typically pass over a victim rather than directly through. The flashover can singe clothing, vaporize sweat and superheat metal buttons and belt buckles.

Not all strikes are direct hits, but most do leave outward marks, whether burns or strange spidery bruises, known as Lichtenberg figures, which trace the path of electricity that forced blood cells out of capillaries.

"A lot of folks bounce back with no injury," said Charles Miramonti, the chief of Indianapolis' emergency medical services and Eskenazi's chief of care integration.

For those with injuries, cardiac and respiratory arrest are the immediate concern, Miramonti said — all that electricity can fry signals and stop the heart. There can be internal and external burns, kidney failure and nerve damage.

"It's really what you don't see that can be concerning," Miramonti said. Only an entry and exit wound may be visible until surgery reveals further damage inside.

Miramonti has seen only one lightning victim, while Miramonti was in residency two decades ago. He also has treated a few victims of electrical accidents, which are less mysterious but involve many similar symptoms.

Andy Isch, who was the trauma surgeon on duty Tuesday when the workers were taken to the St. Vincent trauma center in Indianapolis, said this was the first lightning strike he remembered treating, but with access to good diagnostics, therapy and rehab, people who survive lightning strikes should be OK.